The continued development of physically larger, more complex and higher power semiconductor devices is focusing much attention on the need to package these electronic circuits to provide physical as well as hermetic protection. In addition, the package must help maintain the operating temperature of these devices at a point where their reliability is at an acceptable level. Further, new semiconductor devices may consume hundreds to thousands of watts of power, necessitating the development of new methods of providing power to the circuit, and further increasing the requirement for removing the heat generated by these new higher power devices.
Due to the large variations in the operating temperature or operating environment of the devices, there must not be any large thermal mismatches between the semiconductor device and the packaging materials. This is a critical concern since any thermal mismatch between the semiconductor device and its packaging may induce stresses which can cause a failure in the device itself or in its attachment to the package.
Although the semiconductor devices are becoming larger in size, the interconnections or traces between the logic elements that make up the semiconductor device have become smaller. These traces may be as narrow as one micron wide or less, making them very susceptible to corrosion from moisture or gases in a hostile environment. Intended uses for these larger semiconductor devices still require that they be protected and packaged in such a manner that they be hermetically sealed as well as coolable.
Present semiconductor packaging techniques generally require that a cavity be left surrounding the circuit die itself. Applications requiring hermetic sealing of the semiconductor device require that the package be hermetically tested at levels both higher and lower than atmospheric pressure to insure that no contaminants can enter the cavity surrounding the die. As the circuit becomes larger in size, both the package size and the lid or cover increase in size to accommodate the larger circuit and its interface pads or pins. The increase in area of the lid or cover requires that it be made thicker to reduce deflection under differential pressure. In addition, since the cover is bonded only around its periphery, the stress on the peripheral bond increases with an increase in cover size which could open the bond or damage feed-throughs in the peripheral wall.